Method and apparatus for punching sheet material



- Feb; 21, 1967 METHOD AND APPARATU Filed March 29, 1965 INVENTOR EDMUND F. NOWAK ATTORNEYS United States Patent 3,304,823 METHOD AND APPARATUS FOR PUNCHING SHEET MATERIAL Edmund Franciszek Nowak, Krozauska St. 20/16, Warsaw, Poland Filed Mar. 29, 1965, Ser. No. 443,525 Claims priority, application Poland, Mar. 17, 1965, P 104,192 4 Claims. (Cl. 83-55) This invention is related to a hydraulic press of the two-side operation type, working alternatively with two punching tools, which press is especially suitable for operations of punching and of shaping small parts made of sheet metal or of metal strip.

In the sheet metal working processes, hydraulic presses have been mainly used up to now for deep drawing of sheet metal, while the operations of punching and shaping are usually carried out on mechanical presses of the eccentric type. The main reason for this, is the fact that in-punching operations there is exerted a rapid load on the punching tool in the moment when it contacts the metal sheet, which rapid load causes an impact of the hydraulic liquid of low compressibility on the actuating mechanism of the press. In the case of loads of a considerable value, the said impact of the hydraulic liquid may damage the above mentioned actuating mechanism of the press. On the other hand it is a well known fact, that mechanical presses of the eccentric type-as a result of their considerably higher speeds (number of oppera-tional strokes in a unit of time) in comparison with that of the hydraulic presses-are characterized by the accordingly higher rate of production.

However the results of research work carried out on sheet metal working processes, and especially the research Work on the process of sheet metal punching, have shown that the work on mechanical presses is connected with a considerably shorter service life of punching tools caused by the presence of unavoidable play in the driving mechanisms of the press. Namely, as a result of the transverse play in the said mechanisms there are produced forces which cause buckling stresses in the working part of the punching tool, while as a result of the axial play in the driving mechanisms of the mechanical presses the punching tool is stopped in the moment when it contacts the surface of the metal sheet which is being punched (so called dead .restriking), causing in this way quicker wear of the tool and consequently shortening its service life.

The object of the present invention is to provide a hydraulic press free from the above described disadvantages of mechanical presses as well as of the known until now hydraulic presses applied for carrying out operations of punching of sheet metal. This object has been achieved by providing the hydraulic press according to the present invention with'punching tools, the punching face of which consists of a number of surfaces arranged in two or more horizontal planes, as a result of which the punching tool is gradually driven into the sheet of metal which is being punched and the driving mechanism of the press is loaded in a uniform way, which consequently allows to avoid the above mentioned rapid impacts of the hydraulic liquid. In addition, the press according to the present invention is provided with a dual arrangement of working tables enabling to fix at the same time two independent punching tools and to operate the press in a dual way, as a result of which the punching tools do not do any idle strokes enabling in thi way to obtain the accordingly increased rate of production approaching that of mechanical presses. Furthermore, in the press according to the present invention the play in its mechanisms is considerably smaller in com- 3,304,823 Patented Feb. 21, 1967 parison with the play found in the mechanical presses as a result of which there are obviated buckling stresses and rapid changes of the loading fiorces which allows to increase from ten to twenty times the service life of punching tools. In view of the fact that the cost of a punching tool is comparatively high and forms a considerable part of the total cost of parts punched or shaped on the press, there is obtained in the above way longer service life of the said punching tool which causes consequently a considerable reduction of the cost of production.

A preferred embodiment of the hydraulic press according to the present invention has been chosen for the purpose of illustration and description of the press operation and is shown in an exemplary way in the accompanying drawing wherein reference symbols refer to like parts wherever they occur.

The hydraulic press according to the present invention consists of the following basic units: a frame, a driving unit, a guiding unit and a set of working tables on which are fixed punching tools.

The frame of the press according to the present invention consists of a base 1, of an outer casing 2 and of an inner casing 3 which is connected with the said outer casing. To the upper part of the frame there is secured the stationary working table 4.

The driving unit consists of a cylinder 5 connected with the inner casing 3 and provided with a sealing ring 6 and with a cover 7, and it also consists of a piston 8 fitted in a sliding way inside said cylinder, which piston is connected with a piston rod 9 sliding in guiding sleeves 10 of the inner casing 3.

The guiding unit consists preferably of four columns 11 arranged in a symmetrical way in relation to the axis of the press, and secured to the inner casing 3, while in the upper part said columns are connected each with another by means of the upper stationary working table 12. Further the said guiding unit consists also of sliding sleeves 13 connected at the bottom with the piston rod 9 by means of a plate 14, whereas said sliding sleeves are connected at the top by means of two moveable working tables. The movable working table 15 cooperates with the lower stationary working table, and the moveable working table 16 cooperates respectively with the upper stationary working table 12. In addition, said sleeves 13 are mounted in a sliding way in bearings 17 located in the lower stationary working table 4. Working tables 4, 15, 16 and 12 are provided with known slots 18 of The T-shape cross secton used for fixing punch-ing tools, while working tables 4 and 16 are in addition provided with outlet holes 19 through which are discharged the parts which have already been punched.

The hydraulic press according to the present invention enables to fix in it two sets of punching tools which can .be operated in an alternative way. The die 20 of one of such sets is secured to the lower stationary working table 4 and the punch 21 of said set of punching tools is fixed to the moveable working table 16, whereas the die 20a of the second set of punching tools is secured to the moveable working table 16 and the punch of said second set is fixed to the upper stationary working table 12.

Punches 21 and 21a are made in such a way that the punching face of each consists of a number of surfaces arranged in two or more horizontal planes a and b while the distance between two such surfaces adjacent each to the other is equal to approximately 0.3 of thickness of the metal sheet which i being punched.

The following part of this specification is related to operation of the above described hydraulic press according to the present invention. Two sets of punching tools 20 and 21 and 20a and 21a secured respectively to two pairs of working tables 4 and 15 and 16 and 12 are operating in an alternative way so that when the piston is moving downwards (in the direction of arrow 1 shown on the drawing), there is working the set of punching tools 20 and 21 in the lower part of the press, and at the same time the sheet metal strip is shifted along the surface of the die 20a in the upper part of said press. Whereas, when the piston is moving upwards, there is working the other set of punching tools 20a and 21a, while at the same time the sheet metal strip is shifted along the surface of the die 20 in the lower portion of the press. As a result of the fact, that the punching face of each of the punches 21 and 21a consists of a number of surfaces arranged in different horizontal planes, the punching part of each of the said punches is driven gradually into the sheet metal strip and consequently the driving unit of the press there are applied uniform loads. The research work carried out on the sheet metal work-ing processes has show-n, that after a punching tool has been driven into the sheet metal to a depth h equal approximately to 0.3 of the said sheet metal thickness, nearly all the fibres are broken and next there is only carried out the phase of pushing the punched part into the hole in the die. In view of the above, the most advantageous spacing of the horizontal planes a and b in which there are placed operational surfaces of the punches, is obtained in the case when the distance h between the said surfaces is equal with 0.3 of thickness of the sheet metal which is being punched.

As a result of the above described spacing of punching surfaces in punches, the hydraulic press according to the invention is especially suitable for carrying out the operations of punching and shaping small parts made of sheet metal strip. In effect of the said spacing, the punching part of the punch is gradually driven into the material which is being worked, which enables the use of large multi-operation punching tools for which the total pressing force can considerably exceed the maximum operational pressing force of the press. In addition, as a result of the considerably decreased play in comparison with the play found in mechanical presses, the hydraulic press according to the present invention enables to increase between ten and twenty times the service life of the punching tools. Furthermore due to the dual operation of the press according to the present invention (which kind of operation is enabled by the use of two pairs of working tables), there is obtained proportionally higher production rate of the said press.

The hydraulic press according to the present invention can be applied in sheet metal working processes, especially for the operations of punching and shaping small parts made of sheet metal strips.

What I claim is:

1. A hydraulic press for punching sheet metal comprising, first and second fixed opposed work tables, a movable member mounted between the said first and second fixed work tables and having first and second movable work tables opposed to the first and second fixed work tables respectively, a driving means for reciprocating the movable member so that the said two first work tables are brought together and subsequently the two sec-nd work tables are brought together, said first and sec-0nd fixed work tables being connected to each other by a plurality of guide columns, a sleeve surrounding at least two of the guide columns, said movable member being rigidly connected to the said sleeves, and said driving means comprising a hydraulic cylinder and a piston, and said piston being connected directly to each of the said sleeves for reciprocating the sleeves and the movable member connected thereto.

2. A hydraulic press as claimed in claim 1 wherein at least one of the said first pair of opposed work tables or the said second pair of opposed work tables comprises a plurality of punching tools mounted on one of said work tables and a cooperating die on the other of said work tables, the said punching tools being arranged in at least two sets, the punching ends of the tools of each set being located in a plane substantially perpendicular to the direction of relative movement of the working tables, the said planes of each set being spaced from the planes of each other set by a distance equal to approximately 7 of the thickness of the metal sheet to be punched by the press.

3. A hydraulic press for punching sheet metal comprising at least two relatively movable work tables, a hydraulic cylinder, a piston within said cylinder, said piston connected to at least one of the work tables for moving it towards and away from the other work table, a plurality of punching tools mounted on one of said work tables and a cooperating die on the other of said work tables, the said punching tools being arranged in at least two sets, the punching ends of the tools of each set being located in a plane substantially perpendicular to the direction of relative movement of the working tables, the said planes of each set being spaced from the planes of each other set by a distance equal to approximately of the thickness of the metal sheet to be punched by the press.

4. A method of punching sheet metal comprising the steps of: (1) placing the sheet metal on a die spaced from a member having a plurality of sets of punching tools, (2) moving the member relative to the die so that the punching tools move towards the metal sheet on the die until the punching edges of a first set of tools on the member engage the metal sheet, (3) moving the member towards the metal sheet so that the punching tools of the first set penetrate the metal sheet to a deph of approximately 7 the thickness of the metal sheet at which time the cutting edges of the second set of tools engage the surface of the metal sheet, and (4) moving the member towards the metal sheet so that both the first and second sets of tools completely penetrate the metal sheet, the cutting edges of the first set being spaced from the cutting edges .of the second set at all times by a distance of approximately the thickness of the metal sheet.

References Cited by the Examiner UNITED STATES PATENTS 411,116 9/1889 Aiken 83-620 2,825,405 3/1958 Maass et a1 83639 X 2,843,205 7/1958 Greulich 836l8 X 3,194,099 7/1965 Palter 83622 X WILLIAM W. DYER, JR., Primary Examiner.

J. M. MEISTER, Assistant Examiner. 

4. A METHOD OF PUNCHING SHEET METAL COMPRISING THE STEPS OF: (1) PLACING THE SHEET METAL ON A DIE SPACED FROM A MEMBER HAVING A PLURALITY OF SETS OF PUNCHING TOOLS, (2) MOVING THE MEMBER RELATIVE TO THE DIE SO THAT THE PUNCHING TOOLS MOVE TOWARDS THE METAL SHEET ON THE DIE UNTIL THE PUNCHING EDGES OF A FIRST SET OF TOOLS ON THE MEMBER ENGAGE THE METAL SHEET, (3) MOVING THE MEMBER TOWARDS THE METAL SHEET SO THAT THE PUNCHING TOOLS OF THE FIRST SET PENETRATE THE METAL SHEET TO A DEPH OF APPROXIMATELY 3/10 THE THICKNESS OF THE METAL SHEET AT WHICH TIME THE CUTTING EDGES OF THE SECOND SET OF TOOLS ENGAGE THE SURFACE OF THE METAL SHEET, AND (4) MOVING THE MEMBER TOWARDS THE METAL SHEET SO THAT BOTH THE FIRST AND SECOND SETS OF TOOLS COMPLETELY PENETRATE THE METAL SHEET, THE CUTTING EDGES OF THE FIRST SET BEING SPACED FROM THE CUTTING EDGES OF THE SECOND SET AT ALL TIMES BY A DISTANCE OF APPROXIMATELY 3/10 THE THICKNESS OF THE METAL SHEET. 